In modern aircraft there is an increasing use of various energy sources in order to take some of the load off the engine generators of the aircraft, thus reducing kerosene consumption. For example alternative energy sources, such as solar cells, fuel cells or batteries can be used.
A further approach in modern commercial aircraft consists of making further use of the products or additional products of the energy sources, for example of waste heat, so as to in this way make the energy system and resources system of an aircraft more efficient.